ASSUME           Associate Segment with Segment Register       MASM Directive

    ASSUME  segmentRegister:segmentName,,,
 or
    ASSUME  NOTHING

    Specifies the segment register (segmentRegister) that will be used to
    calculate the effective addresses for all labels and variables defined
    under a given segment or group name (segmentName).

       Notes:     The segmentRegister argument must be CS, DS, ES, or SS.

                  The segmentName argument must be a segment name
                  previously defined with the SEGMENT directive, a group
                  name defined with the GROUP directive, or the keyword
                  NOTHING.  If the keyword NOTHING is used, the previous
                  segment selection is canceled.

                  ASSUME NOTHING cancels the segment selections for all
                  four segment registers.

                  Usage of the segment-override operator (:) will override
                  the segment register specified in the ASSUME directive.